You should see the little triangle used for moving the slider move although the rest of the screen will say the same.

The final step is to click the little triangle, and without releasing it, drag it as far to the left of your screen as possible. You can then release it and refresh the page. Everything should be back to normal and it should be possible to move the sliders again.

The above instructions are assuming you have got the red slider stuck.

If the green slider is stuck, follow the same instructions but with the following changed: